The circuit charges capacitor C₁ up to the limit that 22V zener diode D₃ creates (Figure 1 and Reference 1). You limit the input current with resistors R₁ and R₅. As the input-rectified voltage drops below the C₁ voltage, Q₁ starts conducting and generates a pulse a few hundreds of microseconds long. The coupling of IC₁ makes the response of Q₁ squarer. The rms operating voltage dictates the only requirement for R₁ and R₅. SMD, 1206-size resistors typically withstand 200V-rms operation. This design splits the input voltage between R₁ and R₅, for a total rating of 400V rms. D₃ limits the voltage across the bridge to 22V so that all of the subsequent components can have lower voltage ratings. A 22V zener diode can clamp as high as 30V, so this design uses a 50V, 470-nF ceramic capacitor. Ceramic capacitors have better reliability than electrolytic or tantalum capacitors, especially at higher temperatures. If you prefer a cheaper and smaller 25V part, you can change the zener diode’s voltage to 18V and still have a good margin for safety. Use R₄ to limit the peak current in the LED. The primary limit on the LED current is the slope of the rectified ac input. The gradual slope doesn’t let Q₁ generate current spikes when it discharges C₁’s stored energy.

You can simulate the operation of the circuit in LTspice Version IV (Figure 2 and Reference 2). With a 230V input at 50 Hz, the simulation shows a 17-mA peak in the optocoupler LED. The simulation gives good results with inputs of 90 to 250V, both at 50 and 60 Hz. At 110V and a 60-Hz input, the LED current peak is 8.5 mA, so IC₁ still works. If you need higher LED-drive currents, you can reduce the value of R₃ or increase the value of C₁.